The Scottish comic and star of BBC Two satirical show Mock The Week launched into a lengthy routine about Down’s syndrome children, referring to them as “Mongoloids” and joking that they were destined for an early death.

When he spotted Mrs Smith exchanging words with her husband, he asked why she was talking. Mrs Smith, 37, from Hook, Hampshire, told The Daily Telegraph: “I tried to just show him I was upset and wave him away but he carried on.

“I said, 'Well, my daughter is five and she has Down’s syndrome and we are upset by some of your comments. Instead of saying he was sorry, he said, 'Oh, well, it’s all true, isn’t it?’”

She said Boyle then described it as “the most excruciating moment of his career” before saying “we had paid to come and see him and what should we expect”.

The show took place on Wednesday night at Reading's Hexagon theatre.

Writing on her blog, Mrs Smith said: “I wanted the ground to swallow me up. I have never felt so small, so stupid, so emotional and so pathetic.”

She added: “I expected dry, nasty, crude humour, yes, but unimaginative humour poking fun at the stereotype of people with Down’s syndrome was not something that I expected.”

Mrs Smith’s husband, Kieron, said he was stunned by Boyle’s jokes. “He frequently used words like 'Mongoloid’. He did impressions of the way people with Down’s syndrome talk. One of his jokes was, 'Why is it that everyone with Down’s syndrome has bowl haircuts and bad clothes?’ He came back three times to the idea that people with Down’s syndrome die early.

“It was almost like a throwback to the 1970s.”

In November, Olympic swimming champion Rebecca Adlington complained to the BBC after Boyle joked on television that she resembled “someone who’s looking at themselves in the back of a spoon”.

Boyle, who has since left Mock The Week, was also criticised for making an offensive joke about the Queen. His spokesman declined to comment last night.

What hypocrites. So, it's ok to pay for tickets to see Frankie Boyle joke about rape victims, cancer sufferers, and child abuse, but as soon as he starts making fun of your Mongoloid daughter, you take offence. Sorry Mr and Mrs Smith, but you shouldn't have paid for front row tickets. We all know what Frankie Boyle is like.

In November, Olympic swimming champion Rebecca Adlington complained to the BBC after Boyle joked on television that she resembled ***8220;someone who***8217;s looking at themselves in the back of a spoon***8221;.